Scroll half-way down the page to see screenshots.
For any of this, you'll need some cyan(light blue)/red glasses. 
(or even better (dark)blue/amber(dark yellow) colorcode 3d )

1) Go download the latest iZ3D driver http://www.iz3d.com/t-dcdriver.aspx and install it. 

2) There should be a new iZ3D control panel icon on the bottom right of the screen (next to your clock), double click on it. It should come up. NOTE: If you don't see it sometimes, go into your StartMenu-->Programs-->iZ3D and open the control Panel.

3) Change the output method from "iZ3D" to "Anaglyph" or "Anaglyph Optomized" (which is better & easier on the eyes) and 'Enable Stereo' (to be safe, disable it before you play public online games...especially if the game uses nGuard or punkbuster (like America's Army)

3) You can change any of the shortcuts by clicking on the text boxes and pressing keys. You can change whether the 3Dness is enabled and disabled here. I like to set the default separation to %12, but that's just me.

4) Now...start a game (or other 3D program) that uses DirectX (few OpenGL games work, and some games have an option to use one or the other, but most do not) and the 3D should work.

 There is a better anaglyph than Optomized, called Yellow/blue Anaglyph...but in order to view it you need these glasses , They let you see nearly all the normal colors with much less eyestrain.
Simple explanation: 3D comes from 2 (eye's) perspectives  being combined into one by the brain.
Since the blue filter on the right eye is such a dark blue, you only see blue&black through it, and the amber (darkish yellow) filter you see all colors with a tint of yellow...so your brain quickly figures out to pay attention only to the colors coming through the yellow and only to pay attention to the blue for the right eye's perspective.
In the traditional Red/Cyan, your brain is trying to get color from both...and doesn't work as well, also the eye with the red has to focus differently than the blue which causes retinal rivalry (eyestrain).

Note: Making it 3D requires your PC to basically render two viewpoints in the game, whereas it's usually only has to do one...so it will take more PC power, if games slow down, try turning the settings down in the game or just turning the 3D off.

Pictures:

More info about this 3D driver at it's site: http://iz3d.com/
and it's forums: http://forum.iz3d.com/

What I wrote below is for earlier versions of the 3D driver...

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1) Go download the iZ3D driver (version 1.08) http://www.iz3d.com/t-dcdriver.aspx and install it.

2) There should be a new iZ3D control panel icon on the bottom right of the screen (next to your clock), double click on it. It should come up. NOTE: If you don't see it sometimes, go into your StartMenu-->Programs-->iZ3D and open the control Panel.

3) Change the output method from "iZ3D" to "Anaglyph" and 'Enable Stereo' (to be safe, disable it before you play public online games...especially if the game uses nGuard or punkbuster (like America's Army)

3) You can change any of the shortcuts by clicking on the text boxes and pressing keys. You can change whether the 3Dness is enabled and disabled here. I like to set the default separation to %12, but that's just me.

4) Now...start a game (or other 3D program) that uses DirectX (few OpenGL games work, and some games have an option to use one or the other, but most do not) and the 3D should work...you may or may not notice depending on the game, that some colors in-game that have a lot of red and/or blue look odd or make you ach, if so do the next step.

5) This will add a little yellow to the game when 3D is enabled which effectively gets rid of a little red/blue from the game's colors so that you don't get a headach...it's called optimized anaglyph (it's not a neccessary step)...you enable it by:
go into C:\ProgramData\iZ3D Driver or (depending on your PC) in C:\Documents and Settings\All Users\ApplicationData\iZ3D and open Config.xml and somewhere on or around line 27 you should see <OutputMode Value="0" /> and change the 0 to 1

Note: Making it 3D requires your PC to basically render two viewpoints in the game, whereas it's usually only has to do one...so it will take more PC power, if games slow down, try turning the settings down in the game or just turning the 3D off.

 -Way down are Screenshots-

The following is ONLY for version 1.07...only use it if 1.08 doesn't work at all.

You'll need a pair of cyan/red 3D glasses and a PC with windows (Vista can use DirectX 10...so some new games may not work in 3D, I don't know...but according to their website it is compatible with vista)

1) Go download the iZ3D driver (version 1.07) http://www.iz3d.com/t-dcdriver.aspx and install it.
WARNING: If it asks if you want to install a new version of DirectX, there is a potential that an older game might cease to work...but is very slim...the only game it effected for me was Star Wars:Battlefront II (it slows down and freezes after I ran it once.) EDIT: turned out to be my anti-virus conflicting with it... Newer versions of DirectX cannot be removed from windows once installed...unless you do a system restore backup right before (if you know what that is). But DirectX should be backward compatible...If you do decide not to install the new version of DirectX the 3D will not work; it will probably complain when you try to run games, so just disable the 3D or uninstall the iZ3D driver.

2) Go into where you installed it (usually C:\Program Files\iZ3D Driver), then right click on Config.xml and click on open with and then choose notepad

3) Somewhere in the first half of the file find <NSMode Value="#" />  (it's on line 30 down) and change whatever number it is to 2 for regular Red/Cyan 3D anaglyph or 6 for optimized Red/Cyan 3D anaglyph. Optomised makes everything a little bit more yellow, it is a whole lot easier on the eyes when you have bright blue/red/purple colors, I suggest it.

4) There should be a new iZ3D control panel icon on the bottom right of the screen (next to your clock), double click on it. It should come up.

5) You can change any of the shortcuts by clicking on the text boxes and pressing keys. You can change whether the 3Dness is enabled and disabled here. I like to set the default separation to %12, but that's just me.

Note: Making it 3D requires your PC to basically render two viewpoints in the game, whereas it's usually only has to do one...so it will take more PC power, if games slow down, try turning the settings down in the game or just turning the 3D off.

Note2: If you want Google Earth to work, you have to modify the userprofile.xml in C:\Documents and Settings\{yourusername}\Application Data\iZ3D Driver\ with a text editor. Change Google Earth's <StereoBase Value="#" />'s value to 0.000100 (%0.01). The 3D won't be noticeable till you zoom into things (the grand canyon looks awesome). If you want to get close to buildings it might be a good idea to turn it down even more.